Klaus, I found the Pinboard messages about the change in the KM 88's low-frequency response. The essential one from Mr. Schneider is PBD_11554, dated Sept. 1, 2003 (i.e. from the original arrangement of the Pinboard, before its active part was divided into three sections).

I don't think it would be right to post the message here without permission, but its essential point is, the diaphragm tension was increased (thus reducing the low-frequency response especially in the figure-8 setting) because this improved operational reliability when the microphones were used for speech pickup in radio broadcasting. He said that this change had been made in about 1982.

Not at all. This mic is a rare find and requires love and affection from anyone who would dare to dig inside and sort out the pattern switch. Go ahead and make the connection! Just be sure to report back what you found.

Not on regular base like Klaus, just from time to time, and this wouldn't be a problem. I've seen you're located in Swiss, so - I'm in Gemany.But maybe we're hurting the forum rules, for going on you should PM me, or Klaus.@Klaus, feel free to delete this posting if necessary.

If one needs to manipulate a sample by lowering the pitch, having the f/s very high would keep the artifacts above audibility. I've encounter that very problem; needing a nice explosion I lowered the pitch of a gun shot... then had to high-pass to remove weird rattily sound...

So clearly there is a need to record at higher f/s for many professionals. But does it lead to a better musical experience for a straight acoustic recording?

I have seen research using same music sample as A, with B sent through 20kHz low pass. Subjects picked A, the unfiltered sample.

But the tester provided no info on the filter topology, it could have easily been the problem.

(...) One of them has only fig. 8 pattern working properly, doesn't switch to cardioid and emits a low end buzz when switched to omni.

Cleaning switch contacts to revive missing patterns on KM88 usually do not work: the "switches" are hand-made oddities used only in this model; they do not resemble common switch construction: four solid-core wires are inserted perpendicularly into the switch housing. They serve as the actual contacts which a wiper connects with in one of three positions.

The contact wires, some of which are connected to the head pins via equally stiff wires, are pushed into the ivory-colored plastic body, held in place by a single gold-colored slot screw. The ends of the contact wires are bent 90º to keep them from falling out or slipping through. With time, some of the wires may bend slightly out of contact range for the wiper, and stop conducting.

Two switches are visible in the photo. Foreground: the pattern switch; background, and out of focus: the -10dB switch.Both are the same type three-position switch, and both work on the same funky principle. In your case the -10dB switch may also have lost contact and attenuation can no longer be switched in.

Simple remedy, if you are lucky: carefully pull, twist, and push the ends of the contact wires (their 90º bend is visible in the picture). Some of the wires may need to be de-soldered before you can move them around and try to free their surfaces of corrosion, or straighten them enough to re-establish contact.

A more likely and unfortunately not so easy remedy: carefully remove both switches, after unsoldering ALL connections, straighten the wires, and test for good contact in all three positions before re-installing.

Both remedies can be messy if you pull the wires out too far: they are not easy to reinsert into their slots.